Patients with respiratory insufficiency often require continuous mechanical ventilation with a positive-pressure ventilator. In such patients a tracheotomy or an endotracheal breathing tube is positioned in the patient's main airway with an internal end positioned for exchange of gas within the lungs and an externally protruding end for connection with a ventilator circuit and then a ventilator system. The ventilator system provides heated, humidified, filtered, breathable gas at a prescribed respiratory rate, tidal volume or pressure, and FiO.sub.2 to the patient in repetitive respiration cycles. In each cycle, gas is delivered through the breathing tube into the lungs, and then exhaled gas is permitted to passively flow out of the lungs.
It is frequently necessary or desirable to use a nebulizer to deliver a prescribed amount of liquid medication into the air stream forced through the inspiratory hose of the ventilator circuit. In present practice, to engage the nebulizer to the ventilator circuit, the inspiratory hose is disconnected from the ventilator, a T connector is used to reconnect the inspiratory hose to the ventilator, and a tapered male end of a nebulizer is inserted into the remaining port of the T connector. The nebulizer contains a reservoir for prescribed medications, which are atomized using breathable gas from a separate connection. The medication mist flows from the nebulizer into the inspiratory air stream for the duration of the medication dose. Upon completion of the therapy, the T connector is then removed from the inspiratory side of the circuit. Patients receive medications in this manner from one to twelve times each day.
In order to administer additional nebulizer treatments using existing devices, the practitioner must disassemble the nebulizer in order to add the next medication dose. The residual medication must be emptied from the reservoir and the prescribed dosage introduced. Next the nebulizer is attached to the T connector and placed in the inspiratory side of the ventilator circuit, which requires disconnecting the circuit from the patient. The speed required in safely performing these tasks often results in incomplete removal of condensate, spillage, dropping of the cup-like chamber and consequent delays. Furthermore, if the reservoir is improperly reattached, it results in an ongoing leak in the system. When the nebulizer is removed, the inspiratory hose again is disconnected, the T connector is removed, and inspiratory hose is reconnected to the ventilator.
There are a number of highly undesirable aspects to such methods. Patients who require mechanical ventilation are critically ill. Any disconnection from the machine that they require to sustain their compromised level of health can be life threatening. In fact, some patients are so critically ill that there may be a dramatic deterioration in their vital signs in response to even a momentary break in the ventilator circuit. Moreover, disconnecting certain patients from the positive pressure in the inspiratory hose can cause a partial lung collapse. In addition to the loss of pressure in the system, there is also a risk of contamination and nosocomial infection.
Mucous and condensation frequently build up on the inner walls of the inspiratory hose. Breaking the ventilator circuit exposes hospital personnel to the mucous and possible pathogens. This has become a very important concern with the discovery of the human immunodeficiency virus, the return of certain illnesses, such as tuberculosis, and the widespread development of antibiotic resistant strains of bacteria. In addition to the risk of infection to the health care worker, there is also a risk of cross-contamination as the practitioner moves to other patients. Opening the ventilator circuit also bypasses the defense systems in the patient's upper respiratory system and provides a direct path into the patient's lungs. This often induces a dangerous infection, particularly in patients who are immunocompromised. Moreover, disconnecting the ventilator circuit may cause the endotracheal tube to wobble in the patient's throat, causing considerable discomfort in some cases.
There have been several approaches to addressing some of these issues, some of which are disclosed in U.S. Pat. Nos. 4,805,609, 5,119,807 and 5,388,571 to Roberts and U.S. Pat. No. 4,951,661 to Sladek. These patents disclose nebulizers having connectors for introducing medication from a reservoir into the ventilation circuit. The Roberts patents disclose valve-conduit arrangements to add medication to the nebulizer reservoir and remove residual material so that it is not necessary to open the circuit to service the nebulizer. One limitation of the Roberts devices is that the valves disclosed by Roberts are positioned so that any secretions and condensate from the ventilator circuit could drain into the nebulizer and contaminate it. Another limitation is that the nebulizer remains functionally connected to the ventilator circuit even when it is not in use. As breathable gas passes the mouth of the nebulizer on its way to the patient, some of the air enters the nebulizer instead of traveling to the patient as intended. This can lead to dead space in the circuit as the breathable gas enters the nebulizer reservoir. The only way to functionally close off the Roberts devices from the ventilation circuit is to break the circuit and remove the device, leading to the very problem that Roberts intended to solve.
Sladek discloses a valve that is insertable into the lower opening of a T-shaped connector that is integral with the ventilation circuit. A cap is attached to the valve for closing the lower opening of the valve. When a nebulizer is engaged to the valve through the lower opening of the valve, a valve plate is pushed open to functionally connect the nebulizer to the ventilation circuit. After use, the nebulizer is removed, which closes the valve plate but leaves the lower opening of the valve exposed. The cap can then be placed over the lower opening of the valve to reduce the risk of contamination until the nebulizer is replaced.
The Sladek design requires the practitioners to handle the nebulizer when additional medication is required. This can result in contamination. Also, the short exposure of the valve could result in contamination of the treatment room and the ventilation circuit. Moreover, pushing the valve plate into the air stream causes turbulence and disrupts the air flow to the patient. Several of the Roberts devices also have this disadvantage because components of the assemblies are positioned in the ventilator air path. Therefore none of the known nebulizers disclose means for functionally disconnecting the nebulizer from the ventilator circuit without disconnecting the circuit, exposing the circuit, causing turbulence in the circuit or loss of pressure.
Therefore, a need has remained for ventilator nebulizer assemblies that can be used, maintained and serviced without breaking the ventilation circuit or causing turbulence in the system or loss of pressure.